It has long been a desired and necessary goal to continuously monitor the temperature of storage tanks, particularly those containing flammable and/or combustible materials, such as petroleum products or a wide variety of chemicals. A standard tool used in such measurements has a thermocouple assembly, having wires of dissimilar material which generate a voltage as a function of the temperature around a junction of said wires. Inasmuch as a fire, or excessive temperature, may commence or occur at almost any location in the tank, it is advantageous to determine such occurrence substantially throughout the tank. Rather than provide a plethora of thermocouple junctions, this invention attacks the problem by using a substantially continuous thermocouple cable which is capable of generating a voltage as a function of the highest temperature occurring along its length.